1. Field of the Invention
The invention relates to a device and method for measuring soil strength in a field.
2. Description of the Prior Art
Root-restricting soil layers reduce crop yields in the southeastern United States almost every year due to temporary periods of drought. These root-restricting layers are characterized by a high mechanical impedance. Research has shown that excessive values of mechanical impedance can have detrimental effects on root growth and crop yield [Taylor and Gardner, 1963, Penetration of cotton seedling taproots as influenced by bulk density, moisture content, and strength of soil. Soil Sci. 96(3): 153-156; and Bowen, 1976, Correlation of penetrometer cone index with root impedance. ASAE Paper No. 76-1516, ASAE, St. Joseph, Mich.]. Tillage beneath these layers is an annual practice for most farmers in this region as a method of removing this barrier and improving rooting conditions. Tillage practices facilitate control of the root-restricting layers by a modifying or reducing the mechanical impedance of the soil.
In the past, methods of prescribing tillage operations have often been based on preventive maintenance, rather than diagnostic evidence. However, researchers have recognized the inherent inefficiency of such tillage treatments and have proposed tillage systems where the soil prescribes the necessary tillage treatment to alleviate mechanical impedance problems. These systems require determination of the soil mechanical impedance to determine the tillage needed [Bowen and Coble, 1967, Environment requirement for germination and emergence. TRANSACTIONS of the ASAE 11(12):10-24; and Schafer et al., 1981, Control concepts for tillage systems. ASAE Paper No. 81-1601. ASAE, St. Joseph, Mich.].
Currently, soil cone penetrometers are used to measure the mechanical impedance of the soil and determine the depth of the root-restrictive layer. Typically, measurements are conducted at a few locations within a field and the tillage depth is then set to exceed the deepest root-restricting layer.
The first version of the cone penetrometer was developed by the U.S. Army Corp of Engineers Waterways Experiment Station (WES) to predict trafficability of soil to vehicles (Knight, 1948, Trafficability of soilsxe2x80x94laboratory tests to determine effects of moisture and density variations. Tech. Memo 3-240, 1st supplement. U.S. Army Corp of Engineers Waterways Experiment Station, Vicksburg, Miss.). In brief, the cone penetrometer measures the force required to insert a cone tip into the soil. The force required to insert the tip is converted to cone index by dividing the insertion force by the area of the base of the cone tip. This cone index thus provides an empirical measurement of soil state.
While the cone index provides an accurate measurement of the soil condition at the site of the test, use of the cone penetrometer is not practical for the determination of soil compaction on a large scale field setting [Raper et al., 1999, A tractor-mounted multiple-probe soil cone penetrometer, Applied Engineering in Agriculture 15(4):287-290]. A dense sampling scheme must be used, if the true variation of soil compaction within a field is to be determined. Researchers have attempted to design sampling tools which can determine soil compaction fast enough to permit field scale mapping of soil compaction. Raper et al. (1999, ibid) developed a tractor mounted penetrometer with multiple probes to allow the determination of soil strength profiles quickly across the row. However, while this device increased the penetrometer data collection, the stop-and-go insertion method still was not fast enough to obtain valid data in intensive sampling situations.
Intrusive and non-intrusive methods have been developed for on-the-fly impedance measuring. Ground Penetrating Radar (GPR) and Electrical Conductivity (EC) have been investigated as a means of non-intrusive on-the-fly determination of subsurface soil properties and features [Raper et al., 1990, Sensing hard pan depth with ground-penetrating radar. TRANSACTIONS of the ASAE 33(1):41-46; and Boll et al., 1994, Using ground-penetrating radar to detect layers in a sandy field soil. ASAE Paper No. 94-2513, ASAE, St. Joseph, Mich.].
Several on-the-fly techniques have also been developed which are soil intrusive. Attempts have been made to quantify soil conditions with draft [Young et al., 1988, Quantifying soil physical condition for tillage control applications. TRANSACTIONS of the ASAE 31(3):662-667; and Smith et al., 1994, Using coulters to quantify the soil physical condition. ASAE Paper No. 941040. ASAE, St. Joseph, Mich.]. Smith et al. used coulters to attempt to quantify the soil physical condition. Alihamsyah et al. (1990, A Technique for Horizontal Measurement of Soil Mechanical Impedance. ASAE Paper No. 90-12201. ASAE, St. Joseph, Mich.) developed and tested a horizontal operating blade with an impedance-sensing tip. This prototype tested two tip designs, a standard 30xc2x0 cone and a 30xc2x0 wedge. Both tip designs were tested against a standard vertically operated cone penetrometer. The 30xc2x0 wedge was found to most closely correlate to the standard cone penetrometer. In field tests, Alihamsyah and Humphries (1991, On-the-go soil mechanical impedance measurements. In Proc. Of the 1991 Symp.: Automated Agriculture for the 21st Century, 16-17 December, Chicago, Ill. ASAE, St. Joseph, Mich.) determined that the horizontal blade with a 30xc2x0 wedge was most suitable for further development. More recently, Chukwu and Bowers (1999, Instantaneous multiple depth soil mechanical impedance sensing from a moving vehicle, Unpublished) developed a multiple probe horizontal blade penetrometer with a 30xc2x0 wedge for testing probes. This unit was able to detect impedance values at three distinct depths. Weissbach and Wilde also developed a device similar in concept to that described by Alihamsyah to detect soil compaction on-the-fly (Weissbach and Wilde, 1997, The horizontal penetrograph-big scale mapping device for soil compaction. In Proc. of the 3rd International Conference on Soil Dynamics, 3-7 August, Tiberias, Israel. Faculty of Agricultural Engineering Technion, Haifa, Israel).
While the horizontal penetrometer designs which have been developed have allowed for improved measurement of have impedance, measurements are only taken at discrete depths. There remains a need for a system which would allow impedance to be measured continuously throughout the soil profile.
We have now invented a novel apparatus and method for continuously measuring the soil strength on-the-fly and at different depths. The apparatus includes a downwardly extending probe having an impedance sensor mounted on a leading edge thereof so as to be impacted by the soil as the probe is moved in a horizontal direction therethrough. A reciprocating drive is also provided which is effective for simultaneously oscillating the probe in an up and down movement while it is passing horizontally through the soil. The mechanical impedance exerted upon the sensor is then measured as the probe is passed both horizontally and up and down through said soil, thereby providing a continuous depth-variable profile of the soil strength over a large area.
In accordance with this invention, it is an object to provide an improved on-the-fly apparatus and method for measuring soil strength and compaction.
It is also an object of this invention to provide an on-the-fly apparatus and method for completely measuring soil strength throughout the soil profile over large areas.
Another object of this invention to provide an apparatus and method for rapidly measuring soil strength throughout the soil profile as device is pulled across a field.
Yet another object of this invention is to provide an apparatus and method for continuously measuring soil strength throughout the soil profile.
Other objects and advantages of the invention will become readily apparent from the ensuing description.